The present inventive subject matter relates to holding tanks for the stunning and/or euthanization of fish using electric currents on boats.
The effect of electric currents on fish are well known in the prior art and especially in the general techniques of electrofishing. Electrofishing involves the use of electric currents to attract and/or repel fish with the intent of creating aquatic barriers, sample fish barriers, and/or to increase collection yields.
It has been established that relatively small potentials that are impressed across the body of a fish invoke a flight reaction. Larger potentials result in the alignment of the fish with the electric current, or electrotaxis. Still larger potentials may result in unconsciousness or complete euthanasia of the fish.
Electrofishing has traditionally been used in freshwater lakes and streams and is the subject of U.S. Pat. Nos. 5,445,111; 5,327,854; 4,750,451; 4,672,967; 4,713,315; 5,111,379; 5,233,782; 5,270,912; 5,305,711; 5,311,694; 5,327,668; 5,341,764; 5,551,377; and 6,978,734 which are incorporated herein by reference.
A recurring problem with the examination of laboratory fish is that they tend to be very active. The small size of the fish combined with their activity can impair the researcher from making precise scientific measurements unless the fish is caught and inspected. Thus direct examination of fishes is preferred to “in situ” measurements.
An aspect of fish conservation involves the collection, tagging, and then the subsequent release of tagged fish. If the tagged fish is then captured at a later date, the difference in the fishes' location, health, and size can be compared to when the fish was first caught. Alternately, a group of fish may be caught from a particular area to determine the statistical distribution of each of the fish species. Furthermore, fishes may be caught to determine if a fish is from wild stock or from fishery stock. In all of these cases, when the fish are captured they are typically placed in a holding tank on the boat, and then they are inspected for species and/or tag information, and then returned to the water. When the fish is on the boat it may be in an excited or agitated state due to having been just caught. The agitated state of the fish will typically make it difficult for fish scientists to handle the fish. An agitated fish in the holding tank may also injure other fishes in the same tank. The scientists may also have to accommodate inclement weather conditions on the boat that may include pitching and rolling of the deck.
What is desired is a safe way to anesthetizing fish in the holding tank of a boat as to reduce the amount of stress on the fish while they are inspected and handled. Prior art solutions and techniques to induce anesthesia in fish involve the addition of chemicals to the tank. See U.S. Pat. Nos. 3,551,566; 3,644,625; and 4,807,615; which are incorporated by reference. Chemicals used for anesthesia are expensive to acquire, pose a storage and maintenance problem, and are at risk of degradation. Also the rocking motion of the boat makes dispensing the chemicals into the boat holding tank a difficult process.
Furthermore, there may be environmental restrictions on the discharge of the holding tank contents once a chemical anesthetic in introduced into the holding tank water. If there are restrictions on the discharge of water, this requires that the holding tank water be stored and removed upon the return to dock. The process of storing holding tank water increases the operational cost of the boat due to the increased energy costs.
Therefore, what is desired is an apparatus to immobilize fish and place the fish in an anesthesia state while in a holding tank in the boat. It is also desired that the apparatus pose little or no attendant risk to the researchers or fisherman whom are close to the holding tank. It is also desired that this apparatus can operate without significant modification to the boat infrastructure. It is also desired that this apparatus operate without the use of chemical additives.